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oai:www.repository.cam.ac.uk:1810/3299422023-12-22T14:11:39Zcom_1810_198332com_1810_256064col_1810_214775

Theoretical and experimental secondary electron spin polarisation studies and 3D theory of field emission for nanoscale emitters 10.17863/CAM.77385 Masur, Sabrina Barnes, Crispin 0000000173377245 Ionescu, Adrian 0000000302655281 Edgcombe, Chris Spin-polarised electron beams are an invaluable probe of spin-dependent phenomena in fields of atomic and molecular physics, magnetism and biophysics. For this purpose, this work explores both theoretical and experimental aspects of field emission properties of point-like nano-scale emission sources with special emphasis on their spin-polarising ability. Firstly, the development of a novel multi-scale field emission simulation procedure is introduced and its capability to successfully combine classically calculated boundary conditions with quantum mechanical density functional theory (DFT) simulations are demonstrated. This technique is then applied to two emission tips based on a capped (5,5) carbon nanotube and a small tungsten-pyramid. In so doing, this thesis demonstrates how this novel simulation method can provide insights into material properties, such as the spatial distribution of charge density, the physical distribution and energies of individual orbitals for different applied fields and the changes in total potential energy with varying fields. Secondly, to investigate the interactions between spin-polarised electron beams with ferromagnetic materials experimental work on several magnetic heterostructures was conducted using a spin-polarised low-energy electron microscope. The analysis of the energy and spin-dependent energy loss and newly-developed secondary electron yield experiments have insights into inelastic scattering mechanisms. Measuring the energy-dependent reflectivity in conjunction with DFT simulation further gives indications about the material’s spin-dependent electronic band structure a few electronvolts above the Fermi level. Furthermore, this work includes the design, fabrication, and integration of specialised experimental equipment into a pre-existing ultra-high vacuum system to analyse nano-sized field emitters. As these emitters are based on ultra-thin magnetic Fe and Fe3O4 nano-disks, theoretical studies using micromagnetic simulations were performed to analyse their magnetic behaviour. Based on the resulting phase diagrams suitable dimensions that enable the fabrication of robust spin-polarised field emitter systems, which have a stable in-plane magnetisation and long Néel relaxation times, were found. University of Cambridge 2021-04-01 Thesis Doctoral Doctor of Philosophy (PhD) eng https://www.repository.cam.ac.uk/handle/1810/329942 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/b29fd46a-f006-4755-8c1c-a48790600f07/download dafc1eb21a63e5949cd7e54997cba28c https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/c751ad33-61fb-4c19-89ab-d7ede6bf4db5/download 353adac0d1ebdfd65ab16480263c3c87 https://www.rioxx.net/licenses/all-rights-reserved/ DFT Carbon nanotube Field emission spin polarisation Secondary electrons